This invention relates to a method and apparatus for demodulation and correlation of a code modulated signal with respect to a reference signal.
The demodulation and correlation of a coded signal becomes very crucial in many systems, such as in ranging systems wherein range is essentially determined from the time required for electromagnetic waves to make a round trip between a transmitter-receiver and a turn-around transponder. Ranging systems are primarily useful in tracking spacecraft, but may also be useful in range tracking of aircraft from a ground station or another aircraft. In conjunction with simultaneous operation of three ground stations, enough accuracy may be achieved to implement an aircraft collision avoidance system. Since all of these systems are merely special applications of a ranging system, or are analogous to ranging systems in respect to demodulation and correlation of coded signals, the principles and preferred embodiment of the invention will be described with reference to a ranging system of the type described by Warren L. Martin and Richard M. Goldstein in U.S. Pat. No. 3,659,292.